The US operators of two exchanges for the virtual currency bitcoin have been charged with money laundering linked to the online drugs website Silk Road.

Robert Faiella and Charlie Shrem are accused of trying to sell more than $1.1 million worth of bitcoins to users of the notorious website.

A criminal complaint says the bitcoin exchange violated money-laundering laws by allowing its users to buy drugs and other goods on the site.

Faiella and Shrem are charged with conspiracy to commit money laundering and running an unlicensed money transmitting business, according to a statement from the US Attorney's office in New York.

Shrem, 24, who was also charged with violating the Bank Secrecy Act by failing to file any suspicious activity reports, was arrested on Sunday at John F Kennedy International Airport in New York, officials said.

Authorities did not name the company involved in the scheme, but Shrem is chief executive of BitInstant and a self-described "Bitcoin evangelist" whose venture is backed by Tyler and Cameron Winklevoss, known for a legal spat over the founding of Facebook.

Shrem is also vice chair of the Bitcoin Foundation, a group aimed at promoting use of the crypto-currency.

The Winklevoss brothers said they were "passive" investors in BitInstant and believed it complied with all laws.

"When we invested in BitInstant in the fall of 2012, its management made a commitment to us that they would abide by all applicable laws - including money laundering laws - and we expected nothing less," a statement said.

Faiella, 52, was arrested at his home in Cape Coral, Florida, on Monday, officials said.

The charges come more than three months after federal officials seized the Silk Road website which is used for drugs, hacker tools and other illegal goods and arrested its alleged mastermind, Ross William Ulbricht, who was said to be Dread Pirate Roberts.

Ulbricht, who is awaiting trial in New York, has denied the charges and claims he is not Dread Pirate Roberts.

In November, a message appeared on the social media site Reddit claiming Silk Road had reopened weeks after it was shut down by the FBI.

The bitcoin was invented in the wake of the global financial crisis by a mysterious computer guru using the pseudonym Satoshi Nakamotoby.

While bitcoins have gained in legitimate transactions, the unregulated currency has also been linked to various kinds of criminal activity.